1. Field of the Invention
This invention relates to methods of treating wells. More particularly, a method is provided for consolidating with resins a formation surrounding a well having perforated casing, wherein diversion of the treatment fluids to all perforations is assisted by detonation of an explosive in the wellbore.
2. Description of Related Art
Wells drilled into the earth for producing fluids from subterranean formations are usually equipped with casing. The casing is placed in the wellbore immediately following drilling of the well, cemented in place, and the casing is then perforated over the interval at the depth where fluid is to be produced or injected using perforating means, usually a shaped charge. Tubing is then placed inside the casing, usually with a packer near the bottom of the tubing to seal the tubing-casing annulus, and fluid is produced into the well through the perforations. If the sand in the formation is unconsolidated, individual grains of sand may move along with the fluid and enter the wellbore through one or more perforations. Sand particles in the wellbore may build up and prevent production of fluids from the well and sand particles in produced fluids may cause erosion of the well equipment. Therefore, it is desirable to prevent sand particle movement into the wellbore.
Various types of mechanical filters are placed inside wellbores and used to exclude formation sand particles from wellbores, but in some wells it has been found preferable to form a consolidated, permeable region of particles outside the perforations. This region is created by injecting liquid resin solutions through the perforations, injecting a fluid immiscible with the resin solution to decrease the resin saturation of the sand around the perforations, and polymerizing or allowing the resin to polymerize under conditions that the sand will be permeable. For sand to be permeable, the resin solution must not completely fill the pore spaces of the rock, but it should bridge between grains of the formation and serve as an adhesive between the grains. The fluids entering the well can then flow through the artificially consolidated region and enter the well. In many wells, particularly where the well has produced sand before the resin treatment, it is preferable to pre-pack the near-wellbore region outside the perforations by injecting a slurry of clean, sized sand grains or synthetic grains.
It is important in sand consolidation processes with resins that the grains around each perforation be consolidated. If this is not achieved, then grains from just one perforation can flow into the wellbore and can interfere with production from the well. This requires then that the consolidation process divert an adequate amount of resin to each perforation such that when the resin is polymerized, a consolidated region is formed that can withstand the forces induced by fluid flowing into each perforation
Placing of resins in a formation is normally performed by pumping the resins into the tubing in a well and displacing the resin down the tubing by pumping a displacing fluid which will follow the resin into the formation. It is important that the resin be displaced from the wellbore before substantial polymerization has occurred.
Polymerization of resins is caused by catalysts or curing agents. Catalysts greatly accelerate the rate of polymerization, but do not participate in the reaction. Curing agents react with a component of the resin to form a polymer.
Sand consolidation with resins has been practiced for many years. The problem of diverting resin into each perforation has been approached in recent years by use of "gas generators" placed in the wellbore in proximity to the resin. U.S. Pat. No. 4,936,385 discloses igniting a propellant to generate gas pressure which rapidly forces the consolidating fluid through the perforations and into the subterranean formation.
As set out in Encyclopedia of Chemical Technology, Third Edition, Vol. 9, p. 561, propellants and explosives are chemical compounds or their mixtures that rapidly produce large volumes of hot gases when properly ignited. Propellants react or burn at relatively low rates, whereas explosives react or detonate at much higher rates. Propellants have been made available for use in wells in recent years in the devices which are called gas generators. One such product is sold under the trademark STRESSFRAC. The use of such gas generators is believed to force resin through all perforations and result in a more effective sand consolidation process. Explosives have heretofore been used in wells, primarily for freeing threaded pipe connections when under torque to allow recovery of partial pipe strings ("string shots"). Explosives have been proposed for promoting the reaction of chemicals used to treat wells in U.S. Pat. No. 2,756,826.
While gas generators employing propellants have been disclosed and are believed to provide more effective sand consolidation processes with resins, there remains the need to employ less expensive and more widely available techniques which can be implemented with greater flexibility and employed to divert resin and any other treating fluid used with the resin to all perforations during sand consolidation treatments.